Field of the Invention
This invention relates to a high pressure liquid chromatography apparatus having an improved inline filter connected between the sample injection valve and the inlet to the liquid chromatography column.
In the high pressure liquid chromatography apparatuses, there is provided a sample injection valve for injecting the sample to be chromatographed into the mobile phase. The liquid stream is comprised of the mobile phase and the sample. The liquid stream flows from the sample injection valve into the liquid chromatography column. The column itself is usually provided with an internal sintered frit, as a filter element, at the inlet end thereof to filter out solid particles in the inflowing liquid stream. When the liquid chromatography column inlet filter becomes plugged, it can be cleaned by backwashing, but in many cases the column packing is thereby partially leached out or the packing of the particles in the chromatography column is adversely altered. This renders the column incapable of further use and it must be repacked before it can be reused. Repacking of a liquid chromatography column is relatively expensive and it is desired to minimize the number of times that it must be done. In particular, it has been desired to provide an inline filter between the sample injection valve and the inlet to the liquid chromatography column, which filter can be removed for servicing without disturbing the liquid chromatography column including the packing therein.
It has been proposed to provide a separate inline filter between the sample injection valve and the inlet to a high pressure liquid chromatography column. FIG. 1 illustrates a prior art inline filter for high pressure liquid chromatography columns. This filter comprises a body 1 within which is received an inner piece 2, a filter element 3, an outer piece 4 and a cap 5. The filter element 3 is comprised of a stainless steel frit 6 housed in a polytetrafluoroethylene sleeve 7, which in turn has a gasket 8 surrounding its exterior. The sleeve 7 is received in the opposed recesses in the confronting ends of the pieces 2 and 4. The gasket 8 seals the radial zone between the opposing surfaces of the pieces 2 and 4. This construction is relatively expensive. It possesses a limited filtering area because the filter element 3 is of relatively small diameter. Also, the filter element 3 is usually replaced when it becomes plugged, rather than being cleaned by backwashing. The replacement of the filter element is a significant item of expense in the use of this device.
It is an object of this invention to provide an improved high pressure liquid chromatography apparatus having an improved inline filter, which filter is of simplified construction, which can easily be backwashed without exposing the column bed and which possesses a very low dead volume and good filtration geometry so as to minimize adverse effects on the sharpness of the chromatographic peaks.